TUBERCULOSIS. ^ 685 



byres with tuberculous cows, and Moussu declares that contagion 

 afterwards spreads just as rapidly among goats as among cows. The 

 vaunted great resistance of goats to tuberculosis, formerly so often 

 spoken of, and by some wrongly considered as a condition of immunity, 

 is deceptive, and if tuberculosis is less frequently seen in proats, this is 

 solely because goats enjoy the greatest liberty at all seasons. 



On the other hand, the disease is very rarely conveyed to sheep, 

 even when they are kept for long periods with tuberculous cows. 

 Moussu found that two years of close cohabitation were necessary 

 for its development under these conditions. 



Heredity is a factor of the highest importance in determining the 

 causation of tuberculosis. At the present time a tendency exists to 

 deny this, but such a view is erroneous. 



Observation has clearly shown that tuberculosis is rarely con- 

 veyed from the mother to the foetus, and that practically nonfe of 

 the calves borne by tuberculous mothers react to tuberculin (95 per 

 cent. : Nocard and Bang) ; but even if this is absolutely correct, it 

 only shows that great benefits might be derived if proper sanitary 

 organisation and intelligent hygienic conditions in byres were found 

 everywhere in the country. Unfortunately in practice this is far 

 from being the case. These non-tuberculous calves are left in com- 

 mon contaminated byres, where they rapidly become infected and 

 perpetuate the disease. 



Physiologically these facts are easily explained. The placenta 

 resists the passage of microbes, or at least only allows them to pass 

 under quite exceptional conditions, and practically only when the 

 blood-vessels are affected. As, on the other hand, tuberculosis of 

 the ovaries. Fallopian tubes or uterus generally prevents pregnancy 

 and causes sterility, there is nothing extraordinary in the fact that 

 tuberculosis is not hereditary in the strict sense of the term. The 

 influence of the sire has been invoked, but it has been proved that 

 direct paternal infection is only possible where ulcerating tuberculous 

 lesions of the testicle, prostate, or vesiculge seminales exist. Such 

 conditions seldom or never occur in the sires of domestic animals. 



As a general rule, therefore, it may be said that tuberculosis is 

 not hereditary. New-born animals become infected during the months 

 following birth, either directly through the alimentary tract when the 

 mothers are suffering from mammary tuberculosis, or, perhaps more 

 frequently, through the respiratory and digestive tracts. 



But although microbic infection is not hereditary, it by no means 

 follows that the offspring of tuberculous subjects are as well prepared 

 for the struggle of life as the descendants of healthy subjects. What 

 is transmitted is a greater tendency to contract the disease. 



